Rabson-Mendenhall Syndrome (Patient RM-2) is a rare disorder manifest by severe insulin resistance with mutations in the insulin receptor gene. This patient is a 14 year old boy with, severe insulin resistance, and cardiomyopathy. He is being evaluated for a heart transplant and possible liver and/or lung transplant. We plan to assess his carbohydrate metabolism in vivo using a stable isotope glucose infusion and hyperinsulinemic clamp on 3 occasions: in his baseline state, after a course of immunosupressive therapy, and after liver transplantation.